Composite circuit board

ABSTRACT

A composite circuit board according to an embodiment of the invention includes a first circuit board having a first conductive line and a second conductive line which is longer in length than the first conductive line, and a second circuit board having a third conductive line which is electrically connected to the first conductive line and a fourth conductive line which is electrically connected to the second conductive line and is shorter in length than the third conductive line.

CROSS-REFERENCE TO THE RELATED APPLICATIONS

This application is a national stage of international application No.PCT/JP2009/056390 filed on Mar. 27, 2009 and claims the benefit ofpriority under 35 USC 119 to Japanese Patent Application No. 2008-088851filed on Mar. 28, 2008, the entire contents of which are incorporatedherein by reference.

TECHNICAL FIELD

The present invention relates to a composite circuit board suitable foruse in the mounting of a semiconductor integrated circuit which operatesat high speed.

BACKGROUND ART

With the aim of achieving accurate and efficient transmission ofhigh-speed high frequency signals, heretofore it has been customary toadopt a differential transmission line structure as an internal linestructure of a packaging component for mounting and sealing afast-operating semiconductor device such as IC and LSI or asurface-mount type electronic component. In a differential transmissionline structure of conventional design, a pair of signal conductors arearranged side by side on a main surface of a dielectric substrateserving as a support and as an insulator as well.

In such a differential transmission line structure, a pair of signals inphase opposition are transmitted through a pair of signal conductors.This makes it possible to decrease an amplitude of each signal andthereby achieve the speeding up of data transmission and alsocancellation of external noise.

Conventional differential transmission line structures are typicallydesigned in the form of a parallel microstrip line, and morespecifically a structure in which signal conductors are arranged side byside on a main surface of a dielectric substrate, or the form of aparallel strip line in which such a parallel arrangement of signalconductors assumes an internal layer pattern. In such constructions,however, since the signal conductors are opposed to each other at theirside faces, it follows that its opposed area is so small that theelectrical coupling established between the signal conductors tends tobe not strong enough.

In order to achieve fine-pitch arrangement of electrode terminals in asemiconductor device, for example, in a multilayer circuit boardcomposed of a plurality of dielectric layers, it is desirable to adopt adifferential transmission line structure composed of a pair of signalconductors arranged face to face with each other in a direction ofsubstrate thickness, with an intermediate dielectric layer interposedtherebetween, this is, a broadside-coupled strip line.

In the case of adopting the broadside-coupled strip line, although thenumber of dielectric layers is inevitably increased, since the densityof line in a state of being projected on the dielectric substrate mainsurface is equal to a single length of line, it is possible to achievefine-pitch arrangement. Moreover, the opposed area between a pair ofsignal conductors can be increased. This makes it possible to render theelectrical coupling between the signal conductors stronger than in thecase of adopting the parallel microstrip line, and thereby improve theprospect of enhancement in cross talk characteristics (for example,refer to Japanese Unexamined Patent Publication JP-A 2005-51496).

Incidentally, in a packaging component or an electronic component, apair of signal lines designed in internal layer pattern are led out to asubstrate main surface via a through conductor. This makes it possibleto establish electrical connection with an electrode terminal of amounting circuit board.

However, in the case of adopting the broadside-coupled strip line, sincethe through conductors for use differ in height from each other, when acomposite circuit board is constructed by mounting a packaging componentor an electronic component on the mounting circuit board, considerablevariations in line length will occur in the composite circuit board.This leads to an undesirable increase in the skew (propagation delaytime difference) between differential signals that appears at the outputend, which may result in degradation of transmission performancequality. Furthermore, as the signal speed is increased with consequentshortening of the wavelength of a propagating electromagnetic wave, theamount of phase shift is increased with respect to a single, commonphysical length. That is, the higher is the frequency level, the greateris the extent of skew.

DISCLOSURE OF INVENTION

An object of the invention is to provide a composite circuit boardcapable of reducing quality degradation of signals to be transmittedunder a condition where a dielectric substrate formed withbroadside-coupled strip lines is mounted on a mounting dielectricsubstrate.

A composite circuit board in accordance with one embodiment of theinvention comprises a first circuit board and a second circuit board.The first circuit board includes a first conductive line and a secondconductive line which is longer in length than the first conductiveline. Moreover, the second circuit board includes a third conductiveline which is electrically connected to the first conductive line and afourth conductive line which is electrically connected to the secondconductive line and is shorter in length than the third conductive line.

BRIEF DESCRIPTION OF DRAWINGS

Other and further objects, features, and advantages of the inventionwill be more explicit from the following detailed description taken withreference to the drawings wherein:

FIG. 1 is a perspective view showing a composite circuit board inaccordance with one embodiment of the invention;

FIG. 2 is a plan view of the composite circuit board shown in FIG. 1;

FIG. 3 is a front view of the composite circuit board shown in FIG. 1;and

FIG. 4 is a side view of the composite circuit board shown in FIG. 1.

BEST MODE FOR CARRYING OUT THE INVENTION

In order that the invention may be carried into effect, a plurality ofembodiments thereof will now be described with reference to theaccompanying drawings. Note that such constituent portions as are commonto those of the preceding described embodiment will be denoted by thesame reference symbols, and overlapping descriptions may be omitted.When the description of a given embodiment deals only with a part of itsstructure, then the other parts thereof will be deemed to be the same asthat of the preceding described embodiment.

A composite circuit board 1 comprises a package 2 (a first circuitboard) and a mounting board 3 (a second circuit board). In thisconstruction, there are mounted circular connection pads 4 attached tothe package 2 (a first end and a second end) and circular connectionpads 5 attached to the mounting board 3 (a third end and a fourth end).The circular connection pad 4 and the circular connection pad 5 areelectrically connected to each other by a solder ball 12.

The package 2 is the first circuit board having a dielectric layer 6 andan internal layered conductive line pair 7. The mounting board 3 is thesecond circuit board having a resin substrate 8 and a surface-layer linepair 9.

On the package 2 is mounted a non-illustrated semiconductor device.Moreover, the internal line of the semiconductor device and the internallayered conductive line pair 7 are connected to each other, so that ahigh-frequency signal can be transmitted through the internal layeredconductive line pair 7. The internal layered conductive line pair 7includes an internal layered conductive line 7 b acting as the firstconductive line and an internal layered conductive line 7 a acting asthe second conductive line, thereby constituting a differentialtransmission line structure.

Further, the internal layered conductive line 7 b is composed of aninternal-layer line 11 a acting as a first internal layered conductiveline, a land 11 b, and a through conductor 11 c acting as a firstthrough conductor. Also, the internal layered conductive line 7 a iscomposed of an internal-layer line 10 a acting as a second internallayered conductive line, a land 10 b, and a through conductor 10 cacting as a second through conductor.

The internal layered conductive line pair 7, which is disposed insidethe dielectric layer 6, is built as broadside-coupled strip linesopposed to each other in a thickness direction of the package 2. Theinternal-layer line 10 a and the internal-layer line 11 a are opposed toeach other in the thickness direction, with a dielectric body interposedtherebetween, and are so arranged as to overlap each other when viewedfrom the top face of the package 2.

In order to lead the internal layered conductive line 7 a toward theconnection pad 4, there is a need to form, at an end of theinternal-layer line 10 a, a vertical line portion which extends in thethickness direction for providing connection with the connection pad 4by utilizing the land 10 b and the through conductor 10 c. Also, inorder to lead the internal layered conductive line 7 b toward theconnection pad 4, there is a need to form, at an end of theinternal-layer line 11 a, a vertical line portion which extends in thethickness direction for providing connection with the connection pad 4by utilizing the land 11 b and the through conductor 11 c.

However, for the attainment of the broadside-coupled strip line, theinternal-layer line 10 a and the internal-layer line 11 a are arrangedin line layers having different levels inside the dielectric layer 6.Therefore, the vertical line portion of the internal layered conductiveline 7 a composed of the land 10 b and the through conductor 10 c andthe vertical line portion of the internal layered conductive line 7 bcomposed of the land 11 b and the through conductor 11 c differ inlength from each other.

In the internal layered conductive line 7 b located near a main surface6 a (a first main surface) of the dielectric layer 6 on which is placedthe connection pad 4, the vertical line portion composed of the land 11b and the through conductor 11 c is made short. On the other hand, inthe internal layered conductive line 7 a located away from the mainsurface 6 a of the dielectric layer 6, the vertical line portioncomposed of the land 10 b and the through conductor 10 c is made long.

Moreover, since the connection pads 4 are arranged side by side in anextending direction of the internal-layer line 10 a and theinternal-layer line 11 a, it follows that the internal-layer line 10 ais made longer than the internal-layer line 11 a.

As employed herein, the “length” of a line refers to a distance from oneexternal power input-output portion to the other external powerinput-output portion thereof. For example, in the case of FIG. 1, thelength of the internal layered conductive line 7 b acting as the firstconductive line is the sum of the length of the through conductor 11 cwhich is a distance from the connection pad 4 acting as the externalpower input-output portion to the semiconductor device mounting land 11b and the length of the internal-layer line 11 a which is a distancefrom a boundary between the land 11 b and the internal-layer line 11 ato a part of connection with the semiconductor device. Moreover, thelength of the internal layered conductive line 7 a acting as the secondconductive line is the sum of the length of the through conductor 10 cwhich is a distance from the connection pad 4 to the semiconductordevice mounting land 10 b and the length of the internal-layer line 10 awhich is a distance from the boundary between the land 10 b and theinternal-layer line 10 a to a part of connection with the semiconductordevice.

In a case where a line is led toward the connection pad, as is often thecase in the broadside-coupled strip line, the internal layeredconductive line 7 a and the internal layered conductive line 7 b havedifferent lengths, and this difference in line length results in a skewdifference between differential signals as seen at the output end. Inconsequence, the high-frequency signal transmission performance qualitywill become deteriorated.

Meanwhile, referring to the drawings, in the mounting board 3, thesurface-layer line pair 9 constitutes a differential transmission linestructure.

In the mounting board 3, the connection pads 5 are placed on a mainsurface 8 a (a second main surface) of the resin substrate 8. Theconnection pad 4 of the package 2 and the connection pad 5 of themounting board 3 are electrically connected to each other by the solderball 12. The high-frequency signal propagating through the internallayered conductive line pair 7 of the package 2 is then transmittedthrough the surface-layer line pair 9 via the connection pads 4 and 5and the solder ball 12.

The surface-layer line pair 9 includes a surface-layer line 9 a formingthe fourth conductive line and a surface-layer line 9 b forming thethird conductive line, thereby constituting a parallel microstrip line.

In correspondence with the connection pads 4 of the package 2, theconnection pads 5 connected with the surface-layer line pair 9 arearranged side by side in an extending direction of the surface-layerline 9 a and the surface-layer line 9 b. The surface-layer line 9 a isconnected to a connection pad 5 a (the fourth end) situated toward thefront as seen in the extending direction, whereas the surface-layer line9 b is connected to a connection pad 5 b (the third end) situated towardthe rear as seen in the extending direction. Note that, in thisembodiment, the surface-layer line 9 b and the connection pad 5 bconstitute the third conductive line, and the surface-layer line 9 a andthe connection pad 5 a constitute the fourth conductive line.

The surface-layer line 9 a and the surface-layer line 9 b are arrangedon the main surface 8 a of the resin substrate 8. Accordingly, on themain surface 8 a of the resin substrate 8, the surface-layer line 9 aand the surface-layer line 9 b extend in parallel with each other to alocation short of the connection pad 5 a. In the opposed region betweenthe side faces of, respectively, the surface-layer lines 9 a and 9 b,high-frequency signals are transmitted in a differential manner undermutual electrical connection.

On the other hand, within a region from the location short of theconnection pad 5 a to the connection pad 5 b, the surface-layer line 9 bextend near the connection pad 5 a while skirting there along, and theskirting surface-layer line 9 b makes connection with the connection pad5 a.

Therefore, the surface-layer line 9 b is made longer by the length ofthis extension resulting from the skirting than the surface-layer line 9a; that is, the surface-layer line 9 a and the surface-layer line 9 bdiffer in length from each other. Note that the length of the thirdconductive line is the length extending from one end of thesurface-layer line 9 b connected to the connection pad 5 b to the centerof the connection pad 5 b located at the other end thereof. Moreover,the length of the fourth conductive line is the length extending fromone end of the surface-layer line 9 a connected to the connection pad 5a to the center of the connection pad 5 a located at the other endthereof.

In this way, in the package 2, the attainment of the broadside-coupledstrip line entails the difference in length between the internal layeredconductive line 7 a and the internal layered conductive line 7 b due totheir different levels. Moreover, in the mounting board 3, thesurface-layer line 9 a and the surface-layer line 9 b differ in lengthfrom each other due to the positional difference between the connectionpad 5 a and the connection pad 5 b.

By connecting the package 2 to the mounting board 3 in such a mannerthat the difference in length of the internal layered conductive linepair 7 in the package 2 and the difference in length of thesurface-layer line pair 9 in the mounting board 3 cancel each other out,in the high-frequency signal transmission line as a whole that isconstructed by combining together the internal layered conductive linepair 7 and the surface-layer line pair 9, it is possible to reduce thedifference in line length between two high-frequency lines.

In order to cancel out the length difference between two line pairs, theinternal layered conductive line 7 a which is the longer one of theinternal layered conductive line pair 7 and the surface-layer line 9 awhich is the shorter one of the surface-layer line pair 9 are connectedto each other. Moreover, the internal layered conductive line 7 b whichis the shorter one of the internal layered conductive line pair 7 andthe surface-layer line 9 b which is the longer one of the surface-layerline pair 9 are connected to each other.

This makes it possible to render the sum of the length of the internallayered conductive line 7 b acting as the first conductive line and thelength of the surface-layer line 9 b acting as the third conductive linesubstantially equal to the sum of the length of the internal layeredconductive line 7 a acting as the second conductive line and the lengthof the surface-layer line 9 a acting as the fourth conductive line. Asemployed herein, the wording “substantially equal” means that thedifference between the sums of length falls within 5% of the pulse widthof an electric signal transmitted through the first to fourth conductivelines (or the period of analog waves).

Also in a case where the line composed of the internal layeredconductive line 7 b acting as the first conductive line and the internallayered conductive line 7 a acting as the second conductive line, thethird conductive line 9 b, and the fourth conductive line 9 a are madeof the same material, the sums of the line lengths of them aresubstantially equal.

When viewed from the top face of the package 2 and the mounting board 3,the surface-layer line 9 a, the internal layered conductive line 7 a,and the internal layered conductive line 7 b are arranged in the samestraight line. The connection pad 5 a and the connection pad 5 b arealso arranged in this straight line. Moreover, the internal layeredconductive line pair 7, the surface-layer line pair 9, and theconnection pads 4 and 5 are so arranged that the surface-layer line pair9 connected with the connection pad 5 is opposite in extending directionto the internal layered conductive line pair 7 connected with theconnection pad 4. Under this condition, the package 2 and the mountingboard 3 are connected to each other.

Looking at the package 2 alone, it will be seen that there is adifference in length of the internal layered conductive line pair 7.Also, looking at the mounting board 3 alone, it will be seen that thereis a difference in length of the surface-layer line pair 9. Meanwhile,in the composite circuit board 1 constructed by connecting the package 2to the mounting board 3, it is possible to reduce the difference in linelength between one high-frequency signal transmission line composed ofthe internal layered conductive line 7 a and the surface-layer line 9 aconnected to each other, and the other high-frequency signaltransmission line composed of the internal layered conductive line 7 band the surface-layer line 9 b connected to each other. Theirhigh-frequency signal transmission lines are formed to the differentialtransmission line structure. Accordingly, in the differentialtransmission line structure in itself, the high-frequency signaltransmission performance quality can be improved.

The dielectric layer 6 of the package 2 can be made of any suitabledielectric material so long as it lends itself to use for the formationof an internal multilayer line structure. For example, an inorganicdielectric material such as ceramics and an organic dielectric materialsuch as resin can be used. The specific examples thereof include: aninorganic material such as alumina (Al₂O₃) ceramics, mullite(3Al₂O₃.2SiO₂) ceramics, and glass ceramics; a fluorine resin materialsuch as tetrafluoroethylene resin (polytetrafluoroethylene; PTFE),tetrafluoroethylene-ethylene copolymer resin(ethylene-tetrafluoroethylene copolymer; ETFE), andtetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin(perfluoroalkoxy alkane; PFA); and a resin material such as glass epoxyresin, polyphenylene ether (PPE) resin, liquid crystal polyester (LCP),and polyimide (PI). Moreover, in designing the dielectric layer 6, whilethe shape and dimensions thereof are determined arbitrarily inaccordance with its applications, the thickness in particular isdetermined in accordance with transmission signal frequency andimpedance design.

The internal layered conductive line pair 7 may be made of a metalconductor layer which lends itself to use for high-speed signaltransmission. For example, in a case where a material of the dielectriclayer 6 is made of ceramics, the following examples may be adopted foruse in forming the conductor line: a material obtained by applyingnickel plating and gold plating onto copper, molybdenum-manganese,tungsten, or a molybdenum-manganese metallized body; a material obtainedby applying nickel plating and gold plating onto a tungsten metallizedbody; a material obtained by applying a nickel-chromium alloy and goldplating on tantalum nitride; and a material obtained by applyingplatinum and gold plating onto a nickel-chromium alloy. Moreover, as themethod of manufacturing the line, for example, a thick film printingmethod, various thin film formation techniques, a plating processingmethod, or the like may be adopted for use as a method of construction.The width and thickness of each conductor line are determined inaccordance with transmission signal frequency or impedance design.

While, as is the case with the present embodiment, the resin substrate 8is used for the mounting board 3, the invention is not limited thereto.For example, just like the package 2, an inorganic dielectric materialsuch as ceramics and an organic dielectric material such as resin can beused thereof.

As the electrically conductive member for providing electricalconnection between the connection pads 4 and 5, in the presentembodiment, a solder ball is used. Alternatively, any other electricallyconductive member can be used so long as it lends itself to use forhigh-speed signal transmission. For example, a metal material such asgold, silver, and copper can be used. Moreover, the shape of theelectrically conductive member is not limited to a ball shape, but maybe of a columnar shape or a bump shape, for instance.

For example, the package 2 of the present embodiment is fabricated inthe following manner. In a case where the dielectric layer 6 is made forexample of alumina ceramics, at first, green sheets of alumina ceramicsare prepared. The alumina ceramic green sheets are subjected to apredetermined punching processing to form through holes therein for theplacement of the through conductors 10 c and 11 c. Next, a conductorpaste of tungsten, molybdenum, or the like is charged into the throughhole by means of screen printing. Moreover, conductor lines; that is,the patterns of the internal-layer line 10 a, the internal-layer line 11a, the land 10 b, and the land 11 b are print-coated at predeterminedlocations of the green sheets. Then, the green sheets formed with theirrespective patterns are stacked on top of each other, and the stackedbody is fired at a temperature of about 1600° C.

Moreover, the mounting board 3 is fabricated in the following manner. Acopper-clad substrate is prepared by applying a copper foil on a surfaceof a glass epoxy substrate Grade FR-4, for example. Then, patternformation for the paired outer layer-side line 9 and the connection pad5 is performed on the copper foil by means of a known patterningtechnique such as etching.

On the main surface 6 a of the dielectric layer 6 formed with theconnection pad 4 and on the main surface 8 a of the resin substrate 8formed with the connection pad 5 are disposed solder resists 13 and 14,respectively.

The solder ball 12 is placed on the connection pad 5 of the mountingboard 3, and the connection pad 4 of the package 2 is aligned with thecorresponding connection pad 5. Then, the connection pads 4 and 5 andthe solder ball 12 are bonded together by means of ultrasonic vibration,reflow technology, or otherwise.

As described heretofore, according to the present embodiment, thedifference in length between the first conductive line and the secondconductive line and the difference in length between the thirdconductive line and the fourth conductive line cancel each other out.Accordingly, in the composite circuit board as a whole, the lengthdifference in the differential transmission line structure can bereduced. This makes it possible to reduce the difference in propagationdelay time between differential signals under the state where the firstcircuit board is mounted on the second circuit board, and thereby reducedeterioration in transmission performance quality and qualitydegradation of signals to be transmitted.

According to the present embodiment, it is preferable that the sum ofthe length of the first conductive line and that of the third conductiveline and the sum of the length of the second conductive line and that ofthe fourth conductive line are substantially equal. In this case,quality degradation of signals can be reduced more reliably.

According to the present embodiment, it is preferable that the firstconductive line and the second conductive line are arranged inside thefirst dielectric substrate. In this case, by exploiting the effect ofthe dielectric material, the coupling between a pair of the differentiallines can be strengthened and thus the diffusion of transmission energycan be suppressed, with the consequence that the cross talk between thepair of the differential lines and another pair of differential lines.Moreover, a broadside-coupled strip line can be practically realizedwith ease.

According to the present embodiment, it is preferable that the firstconductive line includes the first internal layered conductive linedisposed inside the first dielectric substrate and the first throughconductor extending from an end of the first internal layered conductiveline to the first end, and that the second conductive line includes thesecond internal layered conductive line which is disposed inside thefirst dielectric substrate so as to align partly with the first internallayered conductive line and is larger in line length than the firstinternal layered conductive line, and the second through conductor whichextends from an end of the second internal layered conductive line tothe second end and is larger in line length than the first throughconductor.

In this way, the second conductive line is made longer than the firstconductive line in terms of both through conductor and internal layeredconductive line. That is, since the second conductive line can belocated so as to cover the first conductive line, it follows that theelectrical coupling between the first conductive line and the secondconductive line can be strengthened.

According to the present embodiment, the first internal layeredconductive line and the second internal layered conductive line are soarranged that mutual aligned regions thereof are overlapped when viewedfrom the top face of the first dielectric substrate. In thisconstruction, it is possible to achieve a broadside-coupled strip linewith ease by coupling the first internal layered conductive line and thesecond internal layered conductive line to each other and therebystrengthen the electrical coupling between the first conductive line andthe second conductive line. It is also possible to reduce the area ofspace required for the placement of the first conductive line and thesecond conductive line, and thereby increase the line density.

According to the present embodiment, it is preferable that the firstinternal layered conductive line and the second internal layeredconductive line are each linearly shaped. By doing so, it is possible toincrease the opposed area between the first internal layered conductiveline and the second internal layered conductive line arranged in anoverlapping manner, and thereby enhance the electrical coupling betweenthe first internal layered conductive line and the second internallayered conductive line.

According to the present embodiment, it is preferable that the fourthconductive line is linearly shaped, and that, when viewed from the topface of the first dielectric substrate, the fourth conductive line, thefirst internal layered conductive line, and the second internal layeredconductive line are arranged in the same straight line.

Moreover, the area of space required for the placement of the firstconductive line, the second conductive line, and the fourth conductiveline can be reduced with consequent increase in the line density.Further, it is possible to allow easy mutual cancellation between thedifference in line length between the first conductive line and thesecond conductive line and the difference in line length between thethird conductive line and the fourth conductive line.

According to the present embodiment, it is preferable that the third endis further arranged in the same straight line described above. By doingso, it is possible to reduce the area of space required for theplacement of the first to fourth conductive lines and thereby increasethe line density.

According to the present embodiment, it is preferable to provide aparallel line portion disposed in parallel with the fourth conductiveline, and an extension. With the provision of the extension, the thirdend and the fourth conductive line can be arranged in the same straightline with consequent increase in the line density.

According to the present embodiment, by virtue of the electricallyconductive member, the first end and the third end, as well as thesecond end and the fourth end, can be mounted with ease.

According to the present embodiment, it is preferable that the first tofourth ends are each formed of a circular connection pad. By doing so, aspherical electrically conductive member such as a solder ball can beused.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription and all changes which come within the meaning and the rangeof equivalency of the claims are therefore intended to be embracedtherein.

1. A composite circuit board, comprising: a first circuit boardcomprising a first dielectric substrate, a first conductive line whichcomprises a first internal-layer conductive line inside the firstdielectric substrate and first through conductor located from an end ofthe first internal-layer conductive line to a first main surface of thefirst dielectric substrate, and a second conductive line which comprisesa second internal-layer conductive line inside the first dielectricsubstrate so as to align partly with the first internal-layer conductiveline and a second through conductor located from an end of the secondinternal-layer conductive line to the first main surface; and a secondcircuit board comprising a second dielectric substrate, a thirdconductive line which is electrically connected to the first conductiveline, and a fourth conductive line which is electrically connected tothe second conductive line and is shorter than the third conductiveline, wherein the second internal-layer conductive line is longer thanthe first internal-layer conductive line, the second conductive line islonger than the first conductive line, and the third conductive line andthe fourth conductive line are located on a same main surface of thesecond dielectric substrate.
 2. The composite circuit board of claim 1,wherein the first conductive line further comprises a first end which islocated on the first main surface and is connected to the first throughconductor, the second conductive line further comprises a second endwhich is located on the first main surface and is connected to thesecond through conductor, the third conductive line further comprises athird end which is located on a second main surface, one of mainsurfaces of the second circuit board, facing to the first main surface,and is electrically connected to the first end, and the fourthconductive line further comprises a fourth end which is located on thesecond main surface and is electrically connected to the second end. 3.The composite circuit board of claim 2, further comprising: a firstconductive member configured to connect the first end and the third end;and a second conductive member configured to connect the second end andthe fourth end.
 4. The composite circuit board of claim 2, wherein thefirst to fourth ends are each a circular connection pad.
 5. Thecomposite circuit board of claim 1, wherein the first internal-layerconductive line and the second internal-layer conductive line are soarranged that mutual aligned regions thereof are overlapped when viewedperspectively from a top face of the first dielectric substrate.
 6. Thecomposite circuit board of claim 1, wherein the first internal-layerconductive line and the second internal-layer conductive line are eachconductive linearly shaped.
 7. The composite circuit board of claim 1,wherein the fourth conductive line is conductive linearly shaped, and,when viewed perspectively from a top face of the first dielectricsubstrate, the fourth conductive line, the first internal-layerconductive line and the second internal-layer conductive line arelocated in a same straight line.
 8. The composite circuit board of claim1, wherein the third conductive line comprises a parallel line portionin parallel with the fourth conductive line, and an extension portionwhich is configured to make the third conductive line longer than thefourth conductive line.